Rotary drive apparatus for a belt tensioner

ABSTRACT

A rotary drive apparatus for a belt tensioner comprises a casing (10) in which a cylinder space (18) is formed, a generally circular disk-shaped rotor (14) mounted eccentrically therein having vanes (26) accommodated in radial slots (24) and a compressed gas source for pressurizing the chambers formed between the vanes, the rotor and the wall of the casing. The chambers are sealed off both with respect to each other and to the casing (10, 12) by a sealing system (30) on the rotor (14). The rotor (14) is mounted on said casing (10, 12) and is rotatable with respect to a shaft (16) and carries at least one pivotally mounted clutch pawl (32) which is engagingly positionable in a clutch toothing (34) on the circumference of said shaft (16).

The invention relates to a rotary drive apparatus for a belt tensionercomprising a casing in which a cylinder space is formed, a generallycircular disk-shaped rotor mounted eccentrically therein having vanesaccommodated in radial slots and a compressed gas source forpressurizing the chambers formed between the vanes, the rotor and thewall of the casing.

A drive apparatus of this kind is already known from German patent 28 14487. Since the rotor of this drive apparatus is directly coupled to thebelt reel of a belt retractor, good utilization is made of the energymade available by the compressed gas source as compared to other typesof belt tensioners in which a linear movement first needs to betranslated into a rotary movement. The compressed gas source, apyrotechnical inflator, pressurizes the cylinder spaces formed betweenthe vanes of the rotor in this known drive apparatus, however, notdirectly but by means of a liquid working medium such as water, since itfails to adequately seal off the rotor in the casing withoutdetrimenting smooth running of the belt reel in the belt retractor bythe coupled rotor.

The invention provides for a rotary drive apparatus for a belt tensionerin which the chambers are directly pressurizable by the compressed gasfrom the compressed gas source and the rotor is not drivingly coupled toa shaft until the compressed gas source is activated, said shaft beingcoupled to the belt reel of the belt retractor so that the rotation ofthe belt reel is not obstructed in normal roll up and roll offoperation.

In the case of the rotary drive apparatus according to the invention,the chambers are sealed off both with respect to each other and to thecasing by a sealing system on the rotor, and the rotor is mounted on thecasing and is rotatable with respect to a shaft and carries at least onepivotally mounted clutch pawl which is engagingly positionable in aclutch toothing on the circumference of the shaft. The sealing systemensures minor losses when the chambers are pressurized directly by thegases given off by the compressed gas source. The clutch pawl arrangedbetween shaft and rotor permits decoupling of the rotor from the shaftin the normal resting position. Preferably, the clutch pawl ismaintained out of engagement with the clutch toothing on the shaft by aspring in a resting position and is moved by the forces of inertia onacceleration of the rotor into engagement with the clutch toothing.

On completion of belt tensioning, the clutch pawl is moved back by thespring into the resting position in accordance with one preferredembodiment so that the rotor is again decoupled from the shaft. The beltreel of the belt retractor connected to the shaft is then again free torotate as if the normal function of the belt retractor were reinstated.This function is important especially when the belt tensioner has beenactivated, e.g. in the case of a minor collision but leaving the carstill capable of being driven so that it can be moved from the road orto a repair shop. In this case, the vehicle occupant is able to buckleup again after having removed the belt. Although the rotary driveapparatus can no longer be actuated, the belt retractor including itsautomatic blocking feature still works, however, as a belt retractorwithout a belt tensioner.

Due to the preferred arrangement of the clutch pawl in a recess in theface of the rotor between two adjacent vanes the coupling function isintegrated in the rotary drive apparatus without magnifying its spacerequirement. In order that the clutch pawl, despite the compactconfiguration, is able to handle large forces, it is preferably crownedrounded at its end facing away from the tip of the pawl and supported bya correspondingly rounded surface of the recess.

Further features and advantages of the invention will be evident fromthe following description and the drawing to which reference is made, inwhich:

FIG. 1 is an exploded view of the rotary drive apparatus in accordancewith a first embodiment;

FIG. 2 is a side view of the rotor of the rotary drive apparatus of FIG.1;

FIG. 3 is a side view of a face of the rotor shown in FIG. 2;

FIG. 4 is a side view of a second embodiment of the rotary driveapparatus according to the invention having, incorporated in the rotor,a clutch pawl which is urged by a helical spring into the restingposition;

FIG. 5 shows the clutch pawl of FIG. 4 in the case of the rotary driveapparatus activated;

FIG. 6 is a perspective view of a part of the rotor indicated in theFIGS. 4 and 5;

FIG. 7 is a side view of a third embodiment in the resting position; and

FIG. 8 is a side view of the third embodiment showing the pawl afterbelt tensioning has occurred.

The main components of the rotary drive apparatus shown in FIG. 1 are acasing, comprising a casing bell 10 and a casing cover 12, a disk-shapedrotor 14 and a drive shaft 16 which is rotatively mounted in the rotor14 and in a bore in the casing cover 12. The rotor 14 is rotativelymounted in a bore in the casing bell 10 and on the shaft 16. The shaft16 has a serration 16a by means of which it is connected to the beltreel of a belt retractor (not shown).

The rotor 14 is accommodated in a cylinder space 18 defined by thecasing bell 10. An inlet 20 is machined in the wall of the casing bell10, through which the gases generated by a compressed gas source can bepassed into the cylinder space 18. This compressed gas source isaccommodated in a side boss 12a of the casing cover 12. Furthermore,recessed in the wall of the casing bell 10 roughly opposite the inlet 20is an outlet 22.

The rotor 14 is provided with three radial slots 24 in each of which avane 26 is shiftably accommodated. Each of these slots 24 is inconnection by its radial inner end via a flow passage with the cylinderspace 18. Between the rotor 14, the vanes 26 and the wall of thecylinder space 18 chambers, capable of being pressurized, are formedwhich are crescent-shaped as a whole due to the eccentric arrangement ofthe rotor 14 in the casing.

The vane 26 which closes off the chamber at the inlet end in thedirection of rotation of the rotor 14 at its front end is fixedlylocated by a shear pin 28 at the casing bell 10 in an extended positionin which its radial outer end sealingly engages the wall of the casingbell 10. As is best evident from FIG. 3, the sealing of the chamberswith respect to each other and with respect to the casing is furtherachieved by a sealing system which substantially comprises a profileseal 30 inserted in each continuous groove in the faces of the rotor.This profile seal extends full-length along the outer circumference ofthe rotor 14 and radially inwards and again outwards about the vanes 26.

Since the rotor 14 is held non-rotatable at the casing by the shear pin28 and the sealing system with the profile seal 30, a clutch is used todrivingly couple the rotor 14 to the shaft 16 upon activation of thecompressed gas source.

This clutch comprises three clutch pawls 32 pivotally mounted on a faceof the rotor 14 and a clutch toothing 34 provided on the circumferenceof the shaft 16. Each of the clutch pawls 32 is accommodated andsupported in a recess 36 of one face of the rotor 14. The clutch pawls32 each feature opposite their pawl tip a crowned rounded end 32a whichis supported in a sliding manner at a correspondingly rounded surface ofthe recess 36. Each of the pawls 32 is pivotally mounted at the rotor 14by a corresponding journal 32b. The pawls 32 are each held in theresting position by a leaf spring 38, the resting position being definedby contact with a surface of the recess 36. In this resting position,the center-of-gravity of each pawl 32, identified by S, is locatedradially inward relative to the journal 32b so that the forces ofinertia act on the pawl with a lever arm and tend to swivel the pawlinto engagement with the clutch toothing 34 when the rotor 14 isaccelerated counter-clockwise. When the rotor 14 comes to rest oncompletion of belt tensioning, the pawls 32 are returned into theresting position by the assigned leaf springs 38. Each of these leafsprings is otherwise clamped in a U-shaped side recess of the rotor 14.

As evident from FIG. 3, the pawls 32 are slightly offset with respect toeach other circumferentially, relative to the tips of the clutchtoothing 34. Due to this offset it is assured that in accidentalcollision of two tooth tips one adjacent clutch pawl attains an optimumengaging position. Furthermore, the special shape of the clutch toothing34 is evident, this comprising teeth have straight tooth flanks andcurved tooth backs. The curved tooth backs facilitate return movement ofthe clutch pawls 32 into their resting position on relative movementbetween rotor 14 and shaft 16 contrary to the direction in which therotor is turned for belt tensioning.

Finally, it is evident from FIG. 3 that the clutch between rotor 14 andshaft 16 could be integrated in the rotary drive apparatus withoutenlarging the size thereof, particularly in the axial direction.

An electric activation sensor (not shown) generates a signal in arestraint situation which, e.g. when a pyrotechnical inflator isprovided, results in the pyrotechnical material being ignited. The gasflows via the inlet 20 into the casing and propels the rotor 14. Thecenter-of-gravity of each clutch pawl 32 is so arranged relative to itsaxis of rotation that the forces of inertia on abrupt acceleration ofthe rotor 14 result in the clutch pawls 32 being pivoted inwards. Afterat least one clutch pawl 32 has mated with the clutch toothing 34, theshaft 16 and the belt retractor are caused to rotate. On completion ofbelt tensioning the leaf springs 38 urge the clutch pawls 32 back intotheir resting position so that the shaft 16 is freely rotatable.

The second embodiment of the rotary drive apparatus shown in the FIGS. 4to 6 differs from that described before merely by the clutch pawl andthe associated springs having a different configuration. In thisembodiment, the clutch pawls 32' are not mounted by a journal 32b at therotor 14, they instead feature an end 50 having a cylindrical outercontour which is pivotally mounted in a complementary shaped recess inthe rotor 14. Each clutch pawl 32' is urged by a helical spring 54 intoits resting position. The helical spring 54 is wound on block,preferably with pretensioning, and is urged into a side recess 56 (cf.FIG. 6) in the rotor 14. The recess 56 having a rectangularcross-section comprises a nose 58 protruding thereinto which serves toarrest the helical spring 54. The helical spring 54 is introducedsideways into the recess 56 as is indicated by an arrow in FIG. 6, thenose 58 thereby being shifted between two adjacent spring turns. The endof the helical spring 54 facing away from the clutch pawl 32' is, inaddition, urged against the corresponding face defining the recess 56,as a result of which the helical spring 54 is already axially andradially fixedly located before placement of the casing cover 12.

By its periphery the helical spring 56 comes into contact with aprotrusion of the clutch pawl 32' and is thereby slightly bent. Onactivation of the rotary drive apparatus, the helical spring 54 bends,as shown in FIG. 5, when the clutch pawl 32' swivels inwards. Oncompletion of belt tensioning, the helical spring 54 urges the clutchpawl 32' back into its resting position shown in FIG. 4.

The embodiment shown in the FIGS. 4 to 6 permits automated assembly ofthe helical spring 54 without the need for complicated guiding aids. Thespring dimensions in the case of this embodiment can be kept very small,helical springs having an outer diameter of 1.6 to 2 mm with a springwire thickness of 0.3 mm having already proved to be suitable.

The embodiment shown in FIG. 7 differs from that shown in FIG. 3 in thatalthough the leaf springs 60 acting on the clutch pawls 32" urge theclutch pawls 32" into the resting position shown in FIG. 7, in whichthey do not engage into the clutch toothing 34, a free end of each leafspring 60 engages a protrusion at the associated clutch pawl 32" suchthat, as shown in FIG. 8, the leaf spring 60 during belt tensioningdisengages from the clutch pawl 32" and is then, for this reason, alsono longer able to disengage clutch pawl 32" from the clutch toothing 34following belt tensioning. As a result of this, the shaft 16 isprevented from rotating. The leaf spring 60 even prevents in theposition shown in FIG. 8 any return swivelling of the clutch pawl 32"and acts as a locking mechanism. Although in this embodiment the normalfunction of the belt retractor is not reinstated following belttensioning, the user is, however, alerted by the blocked tensioningshaft to the belt tensioner no longer being functionable, prompting himto seek workshop assistance.

I claim:
 1. A rotary drive apparatus for a belt tensioner, comprising a casing in which a cylinder space is formed, a generally circular disk-shaped rotor mounted rotatably and eccentrically in said cylinder space and having vanes accommodated in radial slots of said rotor, and a compressed gas source for pressurizing chambers formed between said vanes, said rotor and said casing, said chambers being sealed off both with respect to each other and to said casing by a sealing system on said rotor, a shaft rotatably mounted in said casing and having a clutch toothing on a peripheral surface, and said rotor having at least one pivotally mounted clutch pawl for selective engagement in said clutch toothing of the shaft.
 2. The rotary drive apparatus as set forth in claim 1, comprising a spring holding said pawl out of engagement with said clutch toothing on the shaft, said clutch pawl being adapted to be moved by inertial forces on acceleration of said rotor into engagement with said clutch toothing.
 3. The rotary drive apparatus as set forth in claim 2, wherein said spring disengages said clutch pawl from said clutch toothing following belt tensioning to permit free rotation of said shaft.
 4. The rotary drive apparatus as set forth in claim 3, wherein said spring is a leaf spring secured to said rotor by clamping.
 5. The rotary drive apparatus as set forth in claim 3, wherein said spring is a flexed helical spring.
 6. The rotary drive apparatus as set forth in claim 1, wherein said clutch pawl is mounted in a recess on one face of said rotor between two adjacent vanes and is supported at a wall portion of said recess.
 7. The rotary drive apparatus as set forth in claim 6, wherein said clutch pawl is rounded at its end facing away from a tip portion of the pawl and supported by a correspondingly rounded surface portion of said recess.
 8. The rotary drive apparatus as set forth in claim 1, comprising a plurality of clutch pawls of which at least two are offset with respect to each other in a circumferential direction of said rotor with respect to tooth tips of said clutch toothing on said shaft.
 9. The rotary drive apparatus as set forth in claim 1, wherein said clutch toothing on said shaft has straight tooth flanks and curved tooth backs.
 10. The rotary drive apparatus as set forth in claim 1, wherein at least one of said vanes is releasably locked to said casing by means of a shear pin. 